Traditionally, fuzes used for the initiation of ordnance have relied upon a mechanical system to begin the arming process. The most complex mechanical systems are clockwork driven safety and arming systems. Such systems are activated either with inertia by using a counterweight system that is driven by rotation imparted on the munition by the rifled barrel (For example, see U.S. Pat. No. 6,145,439), or directly by an impeller such as on free fall bombs.
In order for a mechanical system to be reliable, it typically must be large and physically well supported. Such requirements result in fuzes that displace more payload in “man portable weapon systems” where there exists very little room for either the fuze or the payload. For example, in the M406 (40 mm grenade), almost 50% of the projectile is composed of the fuzing assembly.
An alternative fuzing system is also used that includes a less-complex, but many times less reliable, simple impact driven plunger/striker fuze. This type of fuze is initiated by direct contact with the target, which then drives a plunger/striker against a percussion type initiator. If however, insufficient force is imparted against the plunger/striker, then the fuze will fail to initiate. Such an insufficient force can occur for example, if there is a glancing blow or the ordnance strikes a soft target. Because most mechanical fuzes include a combination of both clockwork timing and impact devices, they typically suffer from excessive size, weight and complexity. As a result, their inherent reliability is generally reduced.
If a fuze fails to initiate due to a malfunction, because a glancing blow or a target of insufficient mass failed to initiate the fuze, a very dangerous situation can result. Unexploded ordinance (“UXO”) creates a very persistent and long-term danger. Highly trained specialists are required to neutralize UXO and do so at great personal risk of injury or death. Furthermore, UXO may be left undetected and undisturbed for many months or years later and can cause injury or death to unsuspecting innocent children or adults.